Nickel paramagnetic susceptibility

Fig. X-2.—Curves showing the reciprocal of molar paramagnetic susceptibility of nickel, palladium, and platinum as a function of the absolute temperature.

Exchange interactions in heterodinuclear transition metal complexes have attracted the attention of many researchers in the last few years. Nickel(II)-copper(II) dimers are, in a sense, the simplest systems to be investigated and several complexes containing paramagnetic nickel(II) and copper(II) ions have been reported, as pure complexes2985-2987 or as impurities in a parent lattice.2959,2987"2991 Magnetic susceptibility or EPR spectroscopy has been used to... 

Nickel(IV) complexes have a d6 electronic configuration and are always diamagnetic or weakly paramagnetic with a temperature-independent magnetic susceptibility. The characterization of these complexes is generally based on the stoichiometry and the electrochemical behaviour. 

ESR is subject to some serious limitations. For reasons which need not concern us, resonance may be difficult or impossible to observe if the paramagnetic centre has an even number of unpaired electrons. This means, for example, that ESR can make little contribution to the extensive chemistry of nickel(II). Another problem arises from interactions between paramagnetic centres in magnetically non-dilute samples the resonance may be very broad and uninformative. ESR is best performed on magnetically-dilute samples, which means that we cannot obtain the kind of information furnished by bulk susceptibility measurements about ferromagnetic and antiferromagnetic interactions. 

The heat capacity of anhydrous nickel chloride was studied between 15 to 300 K. The anomalous region associated with the transition from the antiferromagnetic to the paramagnetic state was investigated in detail. A maximum of C° T) was found near 52 K. This temperature corresponds with the temperature of the magnetic susceptibility maximum within the accuracy of the magnetic measurements. 

Below 6 per cent nickel the first observation is that the Weiss constant is zero. The form of the susceptibility isotherm is thus in the case of nickel in no way related to the exchange interaction between adjacent nickel ions. This is not to say that the nickel ions are at infinite magnetic dilution. For nickel in massive nickel oxide the exchange integral, the paramagnetic neighborhood (z), and the number of unpaired electrons are smaller than they are for chromium ions in massive chromia. The quantity. A, is understandably smaller for the case of nickel, and it... 

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